In recent years, battery systems with built-in multiple batteries such as accumulation devices for mobile devices, Power System Stabilizer (PSS), and emergency batteries are attracting attentions. To elicit the performance of these systems, the parameters of the batteries such as state of charge (SOC), state of health (SOH), and maximum chargeable/dischargeable current (allowable charge/discharge current) should be calculated to control the operation of the battery based on the result. Further, the state of charge of each battery should be adjusted adequately.
To achieve these operations, each battery is attached with a battery voltage measurement circuit (cell controller), and a battery controller mounted with central processing unit (CPU) performs the calculation or operation mentioned above based on information transmitted from the cell controller. To perform this calculation with good accuracy, the battery voltage and battery current should be measured with high accuracy. Further, the measurement timings between the voltage and batteries should be close enough because SOC and SOH of the batteries are calculated using correlation between the current and voltage.
The number of communication lines connecting the cell controllers and battery controllers increases if the number of the batteries that are built inside the battery system increases. The manufacturing cost required for wire connections increases as well. Therefore, one idea is to use wireless communication. In such case, an ultrasonic communication method described in PTL 1 below can be contemplated as a communication procedure.
Enormous numbers of communication lines connecting the cell controllers and the battery controllers, can be omitted by allocating a slot for permitting communications to each cell controller and by performing the measurements and communications within this slot as described in PTL 1. This communication shall be at high speed to guarantee a real time calculation.